1. Field of the Invention
The invention relates to a method for evaluating the state of a fuel/air mixture and/or the combustion in a combustion chamber of an internal combustion engine, with sample signals of flame light signals, preferably the flame intensity, with associated mixture states being saved to a database, with flame light signals, preferably the flame light intensity, of the combustion in the combustion chamber being detected and thus being compared with the saved sample signals, and with conclusions being drawn on the state of the mixture in the combustion chamber in the case of coincidence between measured and saved signal patterns.
2. The Prior Art
The development of spark-ignition internal combustion engines and the calibration of engine actuators is subject to precise knowledge of cylinder- and cycle-specific emissions and exhaust gas temperatures. During driving operation, alternating high-load and partial-load sequences can cause reactive gas to flow into the catalytic converter, leading to overheating and finally to damage to the catalytic converter.
When the engine is started and in the case of stationary and especially also transient driving operation, it may occur as a result of delayed evaporation processes and storage effects that the fuel/air mixture is not sufficiently prepared and thus increased emissions, irregular combustion processes or misfiring will occur. The recognition and correction of such operating states is the precondition for low-emission and secure engine operation.
It is therefore important to determine the state of the mixture within the combustion chamber at an early point and to diagnose the cause of increased portions of reactive gas components.
A combustion detector for internal combustion engines is known from U.S. Pat. No. 3,978,720 A, with the flame radiation in the visible and/or infrared range being measured within the cylinder by means of a quartz window in the cylinder wall or in the cylinder head. The detection of the radiation is used for controlling the ignition point or for detecting the speed or misfiring.
WO 97/31251 discloses a fiber-optic pressure sensor for detecting knocking and misfiring in an internal combustion engine. Optical pressure sensors are integrated in a spark plug.
U.S. Pat. No. 5,659,133 A describes an optical high-temperature sensor for the combustion chamber of an internal combustion engine with which variables can be provided for feedback control of the combustion chamber. The optical signals are processed in a transducer in order to detect in real time events such as ignition sparks, start and end of combustion, backfiring and knocking phenomena. The obtained information is used for feedback control of the roughness of the engine and cycle stability. Moreover, statements can be made on combustion temperature and generated emissions through specific flame colours.
EP 0 412 578 A2 discloses a method for recognizing knocking in an internal combustion engine by means of optical combustion sensors associated with the combustion chamber. The flame intensity of the combustion or combustion temperature within the cylinder is measured with the combustion sensors. In the method for recognizing knocking, the combustion light in the respective combustion chambers is detected, with the signals being compared with a defined threshold value. A knocking phenomenon is recognized as such when the signal level provided by the optical sensor lies beneath the threshold value.
JP 63-105262 A further discloses a method for controlling the air/fuel ratio in the internal combustion engine, with the flame light in a combustion chamber being detected by an optical sensor and the fuel quantity supplied to a carburettor being regulated depending on the detected measured value of the optical sensor as corresponds to the air/fuel ratio.
From the specifications FR 2 816 056 A1 and JP 2005-226893 A, a method is known from each for evaluating the state of a combustible mixture, with flame light signals measured during the combustion being compared with sample signals saved to a database and conclusions being drawn on the state of the mixture in the combustion chamber in the case of coincidence between measured and saved signal patterns. In certain cases, the state of the combustible mixture cannot be evaluated precisely enough.
It is the object of the invention to enable a precise monitoring of the mixture state and combustion in a simple way in an internal combustion engine.